1. Field of the Invention
This invention relates to a radiation sensitive film for imaging and monitoring high energy ultraviolet, electrons, X-rays, and neutrons utilizing as the radiation sensitive element; a radiation polymerizable diacetylenic composition, which can be fixed during processing simply by heating after exposure. The invention also relates to convertor-complexed polymeric binder compositions useful in the film for converting high energy incident radiation into lower energy radiation to enhance image formation. Processes for preparing emulsions of radiation sensitive compounds for use in the film are also provided.
2. Brief Description of Prior Art
High energy radiation, including that having energy higher than 4 eV, such as short wavelength UV light, X-rays, gamma rays, electrons, neutrons, and laser radiation are used for a variety of applications, such as curing of coatings and cross linking of polymers, recording images and information, radiography, nondestructive testing and diagnostic and radiation therapy.
Currently, silver halide film, composed mainly of an emulsion of silver bromide/iodide in gelatin is widely used as the film for recording images and information, diagnostic and industrial radiography and monitoring radiation therapy and dose. The main advantages of silver halide film are (1) high spatial resolution, (2) image distribution across a plane which can be obtained from a single exposure and (3) information can be stored permanently. However, silver halide film has many disadvantages and drawbacks: (a) it requires protection from ambient light until fixed, (b) the developing and fixing processes are "wet" and chemical based, and require about five minutes developing time, and the concentrations of individual solutions and chemicals, time and temperature of developing and fixing must be strictly controlled. However, it is desired in the art to have a self-developing, fast, dry fixing film which is not affected by white light. There is further a definite need for an inexpensive, dry-processing film for monitoring high energy radiation dosages, storing information and images, nondestructive testing of industrial parts, medical diagnosis, quality control and verification of radiation therapy procedures which has the advantages and desired features of silver halide film with essentially none of its major disadvantages and drawbacks.
New photosensitive materials are constantly being searched for to provide new film devices. One such group of materials being evaluated are the polymerizable diacetylenes, R--C.tbd.C--C.tbd.C--R, where R is a substituent group, which diacetylenes polymerize in the solid state either upon thermal annealing or exposure to high energy radiation [Adv. Polym. Sci., 63,1 (1984)]. The term diacetylene(s) is used herein to designate a class of compounds having at least one --C.tbd.C--C.tbd.C-- functionality. The solid monomers are colorless or white, the partially polymerized diacetylenes are blue or red, while the polydiacetylenes are metallic being usually a copper or gold color. Polydiacetylenes are highly colored because the "pi" electrons of the conjugated backbone are delocalized. The color intensity of the partially polymerized diacetylenes is proportional to the polymer conversion.
A number of patents have been issued on the synthesis and use of conjugated polyacetylenic compositions. as radiation dosimeters, temperature monitors, and time temperature indicators.
The use of diacetylenes including those having carboxylic acid substituents and their derivatives in photographic and other related arts is disclosed in several U.S. Patents, such as, U.S. Pat. Nos. 3,501,297 and 3,679,738 (issued to Cremeans), U.S. Pat. No. 3,501,302 (issued to Foltz), U.S. Pat. No. 3,501,303 (issued to Foltz et al), U.S. Pat. No. 3,501,308 (issued to Adelman) and U.S. Pat. Nos. 3,743,505; 3,844,791 & 4,066,676 (all three issued to Bloom). These patents disclose dispersions in resin, gelatin, or gum matrices of certain diacetylene crystals for directly imaging photo-reactive compositions. Light exposed areas are evidenced by a color change. A quantum efficiency of 8 to 16 is reported. For the use of diacetylenes in diagnostic X-ray film imaging, significantly high quantum yields are required.
Diacetylenes are not sensitive to visible radiation (long wavelength). Luckey and Boer in U.S. Pat. No. 3,772,027 disclose a diacetylenic photosensitive element containing inorganic salts, such as titanium dioxide, zinc oxide, cadmium iodide, and cadmium sulfide as sensitizers to make the element sensitive to visible radiation. Another similar patent (U.S. Pat. No. 3,772,028) issued to Fico and Manthey discloses a photosensitive element sensitized to visible radiation by the addition of pyrylium salts including thiapyrylium and selenapyrylium salts. Amplification of poorly imaged crystalline diacetylenic compositions is obtained in U.S. Pat. No. 3,794,491 (issued to Borsenberger et al). Faint images are enhanced through post-exposure irradiation. These patents describe formulations and processes for making diacetylenes sensitive to longer wavelength (lower energy) radiation, such as visible so that the film can be used as a photographic film for visible light. However, there is no report on the sensitization of diacetylenes to shorter wavelength (higher energy) radiation, such as X-rays. Such sensitization to higher energy radiation is desirable for making, for example, diagnostic X-ray film.
In order to increase the spatial resolution of images obtained with diacetylenic imaging compositions, Rasch in U.S. Pat. No. 3,882,134, prepared compositions having a much finer grain structure than reported before. He described the use of vapor deposition to facilitate the isolation of fine microcrystals.
Ehrlich in U.S. Pat. No. 3,811,895 disclosed the use of organometallics as sensitizers and the use of such sensitized systems as X-ray film media. Lewis, Moskowitz, and Purdy in U.S. Pat. No. 4,734,355 disclose a processless recording film made from crystalline polyacetylenic compounds. They also disclosed a process of dispersing crystalline polyacetylenic compounds in a non-solvating medium to a concentration of about 2 to 50% polyacetylene crystalline solids and aging said dispersion before drying on a substrate. The sensitivity of the obtained film is low and hence exposure of at least a kilorad of radiation is required to produce the image. Their gelatin/diacetylene mixture requires prolonged aging at low temperature. However, it would be desirable to have a process which does not require aging of the emulsion. Fine crystals (grain size) are desirable for certain applications, such as microfilm and larger crystals can be used for other applications, such as radiation therapy film so that higher radiation sensitivity can be obtained. It is also desirable in the act to have a process to control the diacetylene crystal size.
Guevara and Borsenberger in U.S. Pat. No. 3,772,011 describe print-out elements and methods using photoconductors and crystalline polyacetylenic compounds in contact with a photoconductive layer. Visible images are obtained when these layers are contacted with the application of an electric potential. In the absence of an applied potential, the elements described are stable under normal room-light handling conditions. Guevera et al in U.S. Pat. No. 3,772,011 provides a diacetylenic composition which undergoes direct image-wise photo-polymerization to a highly colored polymeric product when elaborated into a layer of micro-crystals contiguous to a photo-conductive layer. Such polymerization takes place upon exposure during the application of an electric potential across the layers. In some cases, an organic photoconductor may be included in the layer of crystalline polyacetylenes.
Use of diacetylenic compositions for photoresists has been disclosed in U.S. Pat. Nos. 3,840,369; 4,581,315 and 3,945,831.
Patel in U.S. Pat. Nos. 4,235,108; 4,189,399; 4,238,352; 4,384,980 has disclosed a process of increasing the rate of polymerization by cocrystallization of diacetylenes. Patel and others in U.S. Pat. Nos. 4,228,126; and 4,276,190 have described an inactive form of diacetylenes for storing and method of rendering them active prior to use by solvent, vapor and/or melt recrystallization.
Mong-Jon Jun at el (U.S. Pat. No. 3,836,368) describe 2,4-hexadiyn-1,6-bis(n-hexyl urethane), referred to here in as "166", which turns red upon short wavelength UV irradiation (See Example 3 in the Patent). They prepared a coating formulation by adding water to a solution of 166 in polyvinylpyrrolidone in methanol. The UV exposed coating was red, and it changed to a black color after heating at 55.degree. C. and became inactive to UV light. Although 166 is sensitive to UV radiation, the reactivity is not sufficient to use it for applications, such as diagnostic X-ray film. There is a need to increase the reactivity of 166 so that images can be obtained at a lower radiation dose. We repeated the process described by Jun et al and prepared a coating of 166 by the process disclosed in U.S. Pat. No. 3,836,368. We obtained undesirably large crystals and hence an opaque coating. Thus, there is a need in the art for a film device which contains heat fixable diacetylenes, is highly radiation sensitive, preferably transparent and which can be quickly heat fixed in a dry process providing high resolution imaging.
None of the above described patents describe a film which is substantially transparent, highly sensitive to short wavelength UV, X-ray, electron, gamma ray, or neutron radiation and contains a radiation sensitive element composed of at least one polymerizable diacetylenic compound and a convertor which emits radiation of wavelength shorter than 350 nm when contacted with high energy radiation, which when heated becomes fixed and turns into a blue permanent image. Further, use of a polymeric binder e.g., polyethyleneimine, complexed with a convertor material is also not reported. Furthermore, there is no report of a process for making an emulsion of a diacetylene which does not require aging and provides the desired micro-size crystals for preparing transparent films. There are further deficiencies in the prior art with respect to the field of radiation sensitive imaging and monitoring devices as described below.
Silver halide film is not very sensitive to diagnostic X-ray radiation. X-ray images are amplified by placing the film between two fluorescence screens. Intensifying screens are luminescent materials and usually consist of a crystalline host material to which is added a trace of an impurity. Luminescence in inorganic solids usually originates at defects in the crystal lattice (Thomas F. Soules and Mary V. Hoffman, Encyclopedia of Science and Technology, Vol. 14, 1987, pp527-545). The phosphor of the fluorescence screen absorbs X-rays and emits white light. Intensifying screens made with calcium tungstate phosphors have been in use since the time of Roentgen. Around 1972, a new phosphor, gadolinium oxysulfide was developed which emits in the green region and film sensitized to absorb green light was developed. About the same time other phosphors, such as barium fluorochloride and lanthanum oxybromide, which emit in the blue region, were developed. A large number of phosphors have been reported in the literature including terbium activated rare earth oxysulfide (X.sub.2 O.sub.2 S where X is gadolinium, lanthanum, or yttrium) phosphors (T. F. Soules and M. V. Hoffman, Encyclopedia of Chemical Technology, Vol.14, pp 527-545, 1981 and references quoted therein). Gadolinium and tungsten have very high atomic numbers and also have a high energy absorption coefficient. The following combinations have been used for this purpose: GdOS:Tb(lll), LaOS:Tb(lll), LaOBr:Tb(lll), LaOBr:Tm(lll), and Ba(FCl).sub.2 :Eu(ll). A number of patents e.g. U.S. Pat. Nos. 5,069,982; 5,173,611; 4,387,141; and 4,205,234 are representative and have been issued. Among the hundreds of phosphors reported, the literature search reveals that most of them are blue-, green-, or long wave-UV emitting phosphors upon excitation by X-ray. Some of them emit long wavelength blue light, for example, U.S. Pat. No. 4,719,033. No one has so far reported an X-ray screen with a short-wave UV emitting (e.g., wavelength shorter than 275 nm) phosphor.
Convertors/phosphors are usually used as a screen in form of a fine powder dispersed in a polymeric binder. The screens are placed in contact with the emulsion of silver halide film during X-ray irradiation. The prior art does not describe a convertor/phosphor which is in the form of a transparent coating being a solid solution or complex of a convertor with a polymeric binder. The use of these convertors in the under coat, radiation sensitive coat and top coat of the device is also not described.
Polymers are widely used as binders for a variety of applications including paints and X-ray film coating. Though other polymers are proposed, gelatin is a widely used binder for silver halide and other photosensitive materials including diacetylenes. Many polymers have the ability to form complexes with inorganic compounds. However, there is no report on the use of polymeric complexes as binders for the radiation sensitive formulations, such as diacetylenes.
Polyethyleneimine, referred herein as PEl, forms complexes with a number of inorganic and organic compounds, see Polym. Sci., Vol. 15, pp 751-823, 1990 by S. Kobayashi and J. Polymer Science: Part A: Polymer Chem., Vol. 28, pp. 741-758 (1990) by Y. T. Bao and C. G. Pitt. However, there is no report on use of polyethyleneimine and its complexes as binders and convertors for radiation sensitive films.
Emulsions are usually prepared by homogenizing/emulsifying two immiscible liquids, e.g., a water immiscible solvent (e.g., ethylacetate) with water using an emulsifying agent, such as a surfactant. For example, U.S. Pat. No. 4,734,355 describes this type of system, e.g., diacetylene dissolved in water immiscible solvent, such as ethylacetate and emulsified with gelatin solution in water at high speed. As the solvent used is a good solvent for diacetylenes, the method requires that the emulsion be chilled to a low temperature, and the solvent removed and aged. There is no report on making of an emulsion of diacetylenes without a binder and later mixing the emulsion with a binder. Furtiler, there is no report on preparation of emulsion of a radiation sensitive material, such as diacetylene without using a organic solvent. Further, there is no report on quenching the emulsion to a very low temperature, e.g., liquid nitrogen temperature, to freeze the emulsion and inducing crystal growth by thawing the frozen emulsion.